In medical devices, such as wound dressings and ostomy appliances, it is often desired that the device is moisture absorbing and vapour permeable. These devices often comprise a moisture absorbing adhesive coated on a backing layer. Much effort has been made to optimise the moisture absorbing and moisture transporting properties of the construction.
The use of hydrodolloids as absorbers in matrices such as adhesives are well-known in medical devices. The hydrocolloids have superior properties when it comes to absorption of aqueous liquids. Hydrocolloids are e.g. incorporated into absorbent articles such as sanitary napkins, in wound dressings and in ostomy appliances. In U.S. Pat. No. 3,339,546 a bonding composition of polyisobutylene and hydrocolloids is disclosed. Similarly adhesive compositions based on block copolymers are disclosed in U.S. Pat. No. 4,367,732. The adhesives are intended to be used on the skin or the mucosa.
When incorporated into adhesive, hydrocolloids in the form of particles are preferred. Traditionally, hydrocolloids may be any type of water soluble or swellable material. Both natural polymers or derivatives thereof like carboxy methyl cellulose (CMC), pectin and guar gum, and synthetic polymers like polyacrylic acid and polyvinyl pyrilidone (PVP) may be used.
The physical form of hydrocolloids are relatively coarse and irregular particles, typically about 60-100 μm. The traditional hydrocolloids are hence fairly easy to produce by conventional techniques like milling and their coarse size support safe handling in production, by minimising dust formation.
Adhesives with hydrocolloid particles incorporated are well-known in the art e.g. from International Patent Application No. WO 91/09633 which discloses an adhesive composite comprising a swollen hydrocolloid dispersed in a pressure sensitive adhesive matrix. The swollen hydrocolloids are in the form of irregular particles of different shapes. As the hydrocolloid is swollen, the absorbent capacity of the adhesive composite will be limited.
Usually, the hydrocolloid particles are in a dry, non-swollen state when incorporated in the adhesive matrix.
When hydrocolloid particles are incorporated into adhesives, the properties of the resulting adhesives change. Typically the hardness of the adhesive will increase with the addition of hydrocolloid. This is often undesired in medical devices as it is preferred to have soft and skin-friendly adhesives being capable of following the movements of the skin. Furthermore, it is a disadvantage that the processing of the adhesive will be more difficult when working with hydrocolloid-containing adhesives. Due to the increased hardness of the adhesive the tackiness of the adhesive matrix decrease and may prior to addition of hydrocolloids need to be increased by increasing the adhesiveness of the composition, enhancing the risk of damaging the skin when the device is removed.
When a hydrocolloid containing adhesive is used in medical devices, such as wound dressings or ostomy appliances, the hydrocolloids will also serve as moisture transport from the skin or a wound through to the top the device. In order to optimise the moisture transporting properties of the device a very permeable backing layer is normally used. However, a limiting factor in the moisture transport is often related to the interface between the film and the hydrocolloid particles of the adhesive. To achieve an adhesive with moisture transporting properties, an amount of at least 25% w/w hydrocolloids is needed.
From European Patent Application No. 528 191 is disclosed an adhesive composition comprising hydrocolloids. The particle size of the hydrocolloid is between 1-1000 microns, but preferably an average of 50 microns or less. This size is obtained by pulverising the hydrocolloid, and the resulting powder was then sieved to obtain an average particle size of 50 microns or less. Particles obtained by milling or pulverising will be irregular and sharp-edged, and furthermore, handling of very fine particles may be difficult due to dust problems.
DE Patent Application No. 44 34 171 discloses an absorbent adhesive with absorbent particles incorporated. The particle size is between 10 and 1000 microns, or at least smaller than the thickness of the adhesive layer.
The size of the hydrocolloid particles may be a limiting factor on the thickness of adhesive coatings, as the thickness of the coating cannot be smaller than two to three times the particle size. Very thin coatings may be desired in order to achieve a more flexible product as well as the breathability of the product may be enhanced.
Thus, there is still a need for a skin-friendly adhesive composition being capable of absorbing and transporting moisture, having a good tack, being easy to separate and process.
It has surprisingly been shown that by replacing at least a part of the absorbent particles of the adhesive composition with microcolloid particles, improved properties of the adhesive are achieved.